In order to combat rising fuel costs, aircraft engine manufacturers have, in recent years, scrutinized propeller engine systems, and particularly turboprop engines, as alternatives to relatively less efficient turbofan engines. Design of such turboprop engines has focused on propeller system technology. For example, improved performance can be achieved by increasing length and chord size as well as the number of propeller blades.
Each large, fast turning blade must have means for pitch changing and deicing. This may require electrical energy of twenty to forty horsepower in the hub of such turboprop engines. In the past, when electric pitch changing was employed, electrical energy was on the order of a few horsepower. The energy required by the actuating motor could be satisfied by generating electricity in the nonrotating section of the engine and transferring to the rotating hub by means of a slip ring. Alternatively, the rotating boundary itself could be the site of energy generation as shown in Johnston, U.S. Pat. No. 3,900,274. Johnston discloses a magnetic source on the nonrotating engine section which induces a current in a winding mounted on the rotating hub.
Both of the above described means for supplying electrical energy to the hub are workable when energy demands are low. However, both would be unduly heavy if sized to supply power in the twenty to forty horsepower range.
The control means for such turboprop engines are typically located outside the rotating hub. Pitch changing operations are thereby controlled by command signals generated outside the hub. Failure of either the outside power supply or the control means could result in the loss of the pitch changing function.